1. The Field of the Invention
Exemplary embodiments of the present invention generally relate to the field of flexible circuits, and more particularly, to flexible circuits with button plated contacts.
2. The Relevant Technology
Transceiver modules come in a variety of shapes and sizes depending on the specific function they are designed to perform. For example, transceiver modules can be electronic, in which wires are connected to pass data signals, or optoelectronic, in which fiber optic cable is connected to pass data signals. Optoelectronic transceivers typically contain a transmitter optical sub-assembly (TOSA), a receiver optical sub-assembly (ROSA), and a printed circuit board (PCB) with various electrical circuits for controlling the TOSA and ROSA, and for connecting the transceiver module to external devices.
Providing an optimal connection between a TOSA and/or a ROSA and a PCB can be difficult. Within a transceiver module, the TOSA and the ROSA must be positioned within small tolerances to achieve the desired optical performance. Similarly, the PCB must be precisely positioned for its connections to adjacent devices, such as the module housing and external components that connect to the module. Adding a third layer of rigid alignment requirements (the PCB to the TOSA and/or ROSA) makes accurately positioning the devices difficult. In addition to problems with aligning the PCB with the TOSA and/or ROSA, the TOSA and the ROSA often experience vibration and movement as optical cables are moved, attached and detached. The PCB can be damaged or even cracked if it is rigidly attached to the TOSA and/or ROSA at one end and a transceiver module housing at the other. Furthermore, differential thermal contraction/expansion can also cause problems if the PCB is rigidly attached to the TOSA and/or ROSA and optionally to the transceiver module housing.
In an attempt to reduce the above problems, flexible circuits may be disposed between the TOSA and/or ROSA and the PCB to electrically interconnect them while isolating the PCB from vibration or thermal expansion or contraction. The flexible circuit is additionally advantageous in that, during production, the PCB may be mechanically fixed in place while the TOSA and/or ROSA are not, or vice versa. Therefore, a flexible circuit is frequently used for assembly of the module so that variations in device subassembly position do not prevent precise connections and alignments from being made between the TOSA and/or ROSA and the PCB.
In addition to the above, the TOSA and/or ROSA of a transceiver module may include a transistor-outline (TO) header to contain and protect the active devices within the TOSA and/or ROSA. The TO header in turn allows the electrical connection of the active devices in the TOSA and/or ROSA to the PCB, via a flexible circuit board or otherwise. With respect to their construction, TO headers often include a cylindrical metallic base with a number of conductive pins extending completely through, and generally perpendicular to, the base. One conventional method of conductively connecting a flexible circuit to a TO header includes pins on the TO header that connect to reinforced openings on one end of the flexible circuit, TO header pins are soldered to affix the flexible circuit and ensure reliable connections. In turn, the other end of the flexible circuit can attach to “finger” like traces on the rigid PCB, via soldering or otherwise. Such traces are typically aligned in a linear row along the edge of the PCB.
The general construction of such an optoelectronic module 100 is shown in FIG. 1, which illustrates a perspective view of a transceiver module, designated generally at 100. More specifically, the depicted module can be an XFP transceiver module, which is a 10-Gigabit Small Form-Factor Pluggable Module for use in telecommunications networks, local area networks, metropolitan area networks, storage area networks, wide area networks, and the like. XFP transceivers are designed to occupy one-fifth of the space and use one-half the power of prior 10 Gb/s modules.
As depicted in FIG. 1, transceiver module 100 includes TOSA 102, ROSA 104, printed circuit board 106, first flexible circuit 108 and second flexible circuit 110. First flexible circuit 108 interconnects TOSA 102 and printed circuit board 106 while second flexible circuit 110 interconnects ROSA 104 and printed circuit board 106. Also depicted as part of module 100 are housing 112 for containing the electrical components of module 100. Cooperating with housing 112 are a bail release 114 that aids with removing module 100 from a patch panel or other structure that receives transceiver modules and Lucent Connector (LC) cable receptacles 116 for receiving and securely attaching LC cables to TOSA 102 and ROSA 104. In the illustrated embodiment of FIG. 1, first flexible circuit 108 connects to TOSA 102 at first interface 118 and connects to printed circuit board 106 at second interface 120. ROSA 104 attaches to second flexible circuit 110 at a third interface 122 via a TO-Header soldered pin interface. Second flexible circuit 110 connects to printed circuit board 106 at fourth interface 124.
One problem associated with the design shown in FIG. 1 is that the connections between flex circuit 108, PCB 106 and TOSA 102 can be difficult and time consuming to make. Likewise, the connections between flex circuit 110, PCB 106 and ROSA 104 can also be difficult and time consuming to make. In an attempt to speed up the process and reduce processing time, a “hot bar” process is used to connect, for example, flex circuit 108 to PCB 106.
With reference to FIG. 2, a conventional hot bar process can be used to attach, for example, PCB 106 to flexible circuit 108. One basic structure used to perform this process is shown in FIG. 2 as reference numeral 150. To perform the process, a pad 156 of PCB 106 is brought into close proximity with a corresponding pad 152 of flexible circuit 108. Pads 152 and 156 are shown as having a thickness for the purpose of illustration only. A layer of solder 154 is disposed between pads 152, 156. When a heat source 158 is applied to flexible circuit 106, as illustrated by arrows A, solder 154 liquefies and begins to flow.
Unfortunately, with process 150, the thickness of the solder joint thus formed varies depending on how much heat and pressure was applied. On parts of pad 152, the solder joint is relatively thick and on other parts it is relatively thin. This adversely affects the mechanical strength of the solder joint. In addition, this adversely affects the electrical transmission properties of the solder joint.